To ensure the valve provides adequate sealing, the valve plate must be thrust with high pressure against the valve seat, and as a result the moving member of the valve must be driven by powerful means.
For example, one prior art reduced pressure valve essentially comprises: a hollow body divided into first and second portions by an internal partition, with the first portion being provided with a first opening for connection to an enclosure to be evacuated and with a second opening for connection to the aspiration side of a vacuum pump; a moving valve plate disposed inside the first portion; a spring urging the valve plate to close the first opening; a rod having one end connected to the valve plate and passing through the internal partition; and a piston which is connected to the other end of the rod, and which divides the second portion into a first chamber and a second chamber which are sealed from each and being in communication with the outside.
To open this prior art valve, an auxiliary vacuum pump is required, e.g. a membrane pump, together with its drive motor to overcome the force of the spring which force may be large.
This equipment thus requires bulky auxiliary equipment which may occupy two to three times the volume of the valve itself.
Preferred implementations of the present invention mitigate this drawback and provide a valve which operates on reduced pressure without requiring bulky auxiliary equipment.